Studies in the Physiology of Parasitism. IX. The 
Effect on the Germination of Fungal Spores of 
Volatile Substances arising from Plant Tissues. 
BY 
WILLIAM BROWN, M.A., D.Sc. 
( From, the Department of Plant Physiology and Pathology , Imperial College of Science 
and Technology , London .) 
I N the course of an investigation of the exosmosis of nutrient substances 
from plant tissues into the infection drop (1), the observation was made 
that spores of Botrytis cinerea germinate better when petals of Rosa centi- 
folia are placed in the same Petri dish, but out of contact with the wafer 
drops in which the spores are sown, than when they are absent. This re- 
mained an isolated observation for some years. When the subject was 
again taken up it was found that the capacity to stimulate 1 and, more 
generally, to influence the germination of fungal spores in some way or 
other by means of some volatile emanation could be demonstrated in the 
case of a large number of plants. 
To the writer the main interest of these observations lies in the possible 
effect which volatile substances of plant origin may have in the establish- 
ment or non-establishment of fungal attack. It is felt, however, that it will 
be impossible to estimate their importance in questions of immunity and 
susceptibility until certain other nutritional problems have been dealt with. 
For this reason a more intensive study of these effects, and especially in 
relation to the chemical nature of the substances which produce the pheno- 
mena observed, has been postponed for the time being. Though the present 
account is of a somewhat preliminary nature, nevertheless enough .work 
has been done to show that volatile substances of plant origin may play a 
1 The term 1 stimulation ’ is here applied in the simple descriptive sense of increased germina- 
tion ; for the converse effect of reduced germination the word * retardation ’ is generally used. It is 
fully recognized that effects of ‘ retardation ’ are also effects of ‘ stimulation in particular of too 
strong stimulation in the usual physiological sense. Further, the use of the term ‘ stimulation 5 is 
not to be taken as prejudging the question as to whether the results are of a stimulatory as contrasted 
with a nutritional nature. • The distinction between stimulus and nutrient is more easily drawn in 
theory than in practice, and in the case of the substances considered in the present paper — which 
most probably contain carbon and thus may enter directly into the carbon metabolism of the fungus — 
any satisfactory distinction between stimulus and nutrient is at present impossible. 
[Annals of Botany, Vol. XXXVI. No. CXLIII. July, 1922.] 
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